Turbines are widely used in a variety of aviation, industrial, and power generation applications to perform work. Each turbine generally includes alternating stages of peripherally mounted stator vanes and rotating blades. The stator vanes may be attached to a stationary component such as a casing that surrounds the turbine, and the rotating blades may be attached to a rotor located along an axial centerline of the turbine. A compressed working fluid, such as steam, combustion gases, or air, flows along a gas path through the turbine to produce work. The stator vanes accelerate and direct the compressed working fluid onto the subsequent stage of rotating blades to impart motion to the rotating blades, thus turning the rotor and performing work. Compressed working fluid that leaks around or bypasses the stator vanes or rotating blades reduces the efficiency of the turbine. As a result, the casing surrounding the turbine often includes an inner shell of shrouds or shroud segments that surround and define the outer perimeter of the gas path to reduce the amount of compressed working fluid that bypasses the stator vanes or rotating blades.
Continuous exposure of the turbine shroud to the gas path may result in excessive heating and/or failure of the outer surface of the turbine shroud, particularly in the case of turbines that operate with high temperature compressed working fluids, such as gas and steam turbines. Although several systems and methods have been developed to cool the turbine shroud, the ability to efficiently and cost-effectively cool the outer surface of the turbine shroud remains difficult. For example, U.S. Pat. No. 5,957,657 describes a method for forming a cooling passage in a turbine shroud that includes forming a groove in the outer surface of the turbine shroud and covering the groove with a plug to form the cooling passage along the outer surface. Although the outward facing cooling passage may be easily machined into existing shrouds, continuous exposure of the plug to the gas path and associated temperature changes in the gas path may weaken and/or damage the plug, possibly introducing damaging debris into the gas path. U.S. Pat. No. 7,284,954 describes a turbine shroud that includes a plurality of fluid passages machined into the turbine shroud, and a cooling fluid, such as compressed air, may be supplied through the various fluid passages to cool the outer surface of the turbine shroud. Although U.S. Pat. No. 7,284,954 overcomes the previous disadvantages of exposing a plug to the gas path, the machining required to form the fluid passages may be relatively difficult, time-consuming, and expensive to accomplish. In addition, although the fluid passages communicate the cooling fluid to the outer surface of the turbine shroud, the relatively high flow rate of the cooling fluid through the fluid passages under-utilizes the heat capacity of the cooling fluid. As a result, continued improvements in systems to cool turbine shrouds and methods of manufacturing turbine shrouds would be useful.